Currently, laser perfusion imaging (LDPI) is undergoing a technology shift from scanning beam perfusion imagers to
whole field systems. The latter can be subdivided in laser Doppler methods systems based on high speed CMOS
cameras, and laser speckle contrast analysis (LASCA) technologies using slow imaging arrays, mostly CCD-based. In
scanning beam systems, a collimated laser beam scans the tissue with diffusely back reflected light being captured with a
single detector. In whole field systems a large tissue area is illuminated, and the reflected light is imaged onto an array
and captured at once. Unlike scanning beam systems, both whole field methods enable perfusion imaging at video rate.
In this study we experimentally compare the scanning beam LDPI principle with whole field LDPI, using Intralipid
phantoms. For the tissue phantoms, the Monte Carlo simulation technique will be used as a reference. From
measurements on Intralipid phantoms compared to Monte Carlo, we conclude that in whole field LDPI the flux image,
representing the first order moment of the power spectrum of photocurrent fluctuations is much closer related to real
perfusion than for scanning beam systems. This difference can be explained in terms of the different behaviour of
dynamic speckle patterns generated in both methods, in response to varying tissue optical properties.
Recently, various groups have developed wide field laser Doppler perfusion imaging systems based on high speed
camera's. The limiting factor for the frame rate and measurement duration in whole field laser Doppler perfusion
imaging is the speed of transfer and analysis of data. We present an algorithm for calculating perfusion estimations with
much lower demands for data storage and computational effort than the conventional FFT-based method. Our algorithm
works in the time domain and estimates perfusion through simple time differentiations and multiplications of speckle
image values. The algorithm is partly based on mathematical reasoning, and partly on a hypothesis that cannot be proven
with rigorous mathematics. We will compare our algorithm with the frequency-domain counterpart for phantom studies
involving static and dynamic media, and in vivo experiments on human skin. It is found that both algorithms, applied on
the same dataset, approximately give the same perfusion estimations. The random differences are similar to the random
variations found in tissue perfusion. Systematic differences between the algorithms smaller than 15% are found. The
algorithm is currently twice as fast as the FFT-counterpart. Another advantage is that our algorithm can be included in a
moving average scheme, where a new perfusion value can be determined based on the previous value and a small
number of new raw speckle images.
Laser Speckle Contrast Analysis (LASCA) and Laser Doppler Perfusion Imaging (LDPI) are techniques widely
used for determining cerebral blood flow, the skin perfusion in burns and during drug uptake, and cerebral blood
flow.
Both techniques are based on the dynamic speckle pattern on the detector generated by the sample under
investigation. In LASCA the speckle pattern is recorded using a long exposure time (i.e. milliseconds) resulting
in a blurred image, the perfusion map is obtained by calculating the contrast in the blurred image over small
areas (e.g. 5x5 or 7x7 pixels). In LDPI a series of speckle patterns are recorded using a short integration time
(i.e. microseconds). By determining the power spectrum of the intensity fluctuations per pixel and calculating
the first moment, the perfusion map is obtained.
Because both techniques are based on the same phenomenon we show it is possible to relate the outputs
of LASCA and LDPI. Such a connection is important because of the growing interest in LASCA techniques.
Here we perform the first steps in the comparison of both techniques, using both simulated signals and signals
measured with a high speed camera which can perform LDPI as well as LASCA.
The technique of Laser Doppler Perfusion Imaging (LDPI) is widely used for determining cerebral blood flow or
skin perfusion in the case of burns. The commonly used Laser Doppler Perfusion Imagers are scanning systems
which point by point scan the area under investigation and use a single photo detector to capture the photoelectric
current to obtain a perfusion map. In that case the imaging time for a perfusion map of 64 x 64 pixels is around 5
minutes. Disadvantages of a long imaging time for in-vivo imaging are the bigger chance of movement artifacts,
reduced comfort for the patient and the inability to follow fast changing perfusion conditions.
We present a Laser Doppler Perfusion Imager which makes use of a high speed CMOS-camera. By illuminating
the area under investigation and simultaneously taking images at high speed with the camera, it is possible to
obtain a perfusion map of the area under investigation in a shorter period of time than with the commonly used
Laser Doppler Perfusion Imagers.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.